Hydrogeological Importance of Bedrock Sediments to the Community and Growth of Sugar Cane in Fadama Rake Area of Madagali, Northeast Nigeria

摘要

Thirty Vertical Electrical Sounding (VES) points were sited on the alluvial plain of Madagali fadama area. This was aimed at establishing the lithological character of the drainage plain and its contributions to the growth of sugar cane. 1X1D shareware package was used to interpret the curves. Over the floodplain, potential recharge water into the subsurface units probably takes place through migration routes of coarse-grained colluvial deposits which act as effective soak away for surface runoff. The nature of the basin and/or the transporting routes conditioned the thickness of the surface layer. Effects of near surface bedrock or buried granite boulders disengaged from nearby hills are demonstrated by sandwiching of the bedrock in place in the second resistivity layer. Closely spaced iso-ohmic contour values suggest presence of different types of sediments within the medium of deposition. The high thickness associated with this horizon suggests that the basin was large enough to contain the sediments. Clay materials in the third resistivity layer occur as lens bodies within sandy material. Clay free sand and gravel constitute a great proportion of the stratigraphy. Parts of the bedrock's summits that approached the surface at two separate places are resistant to weathering. Thicker sediments were available where sandy and gravelly materials prevailed. Gradual increases in thickness of the sediments suggest a gentle sloping depositional basin. Sharp gradation of the grain size from clay to bedrock within the fourth resistivity layer depicts a basin that did not permit transportation of the material far from its source. Three zones of groundwater potentials were identified from the total longitudinal conductance and the porosity maps of the area. These were based on the weathered products that constitute the aquifer zone where thick saturated sand and gravel are associated to deep aquifer development and thin saturated sand and gravel to bedrock highs. The contributions of the overburden to sourcing groundwater probably attracted Madagali community to the area and promote the growth of sugar cane in the fadama.